Wireless communication systems present particular difficulties for servicing emergency 911 calls. With the conventional public switched telephone network and land-line services, the location of terminal equipment is fixed and can be pinpointed rather easily. The terminal equipment has a telephone number that is associated with a fixed location. Because a wireless communication system is designed to provide communications service to mobile devices, the location of the devices at any one time is difficult to determine.
A number of techniques have been developed to accurately locate a mobile device that has placed an emergency 911 call. For example, some systems employ triangulation methods to locate the device by comparing signal strength, time-of-arrival, and/or angle-of-arrival information from multiple antennas. Other systems employ global positioning devices within the handset to locate the mobile device.
One difficulty that arises for known solutions is operation within certain facilities. Many facilities present problems for wireless signals and require that an in-facility signal distribution system be employed to provide adequate wireless reception and coverage within the facility. Signal distribution is often accomplished by providing an antenna distribution system that is coupled to a base station of the wireless communications system. In large facilities, this can mean that the only information that the wireless communications system will have regarding a call is that it originates within the facility. Angle-of-arrival or signal strength techniques of locating the mobile device are ineffective within such a facility.
Accordingly a need exists for more accurately locating a mobile device originating an emergency 911 call from within a facility that employs a distributed antenna system.